Construction of novel phycocyanin conjugated chitosan-TiO2-Fe3O4 nanoparticles for Lactobacillus retainment and application in cyclic batch fermentation.

INTRODUCTION: Many industries struggle to maintain culture during the repetitive batch fermentation process and also involve various downstream processing steps to separate microbial cells from the product. Hence, our study was focused on synthesising a novel biomaterial, a protein-conjugated magnetic nanoparticle, for Lactobacillus sp. retention and reuse and to reduce the process of cell-membrane filtration. METHODS: Experimental studies were conducted to synthesise chitosan-coated phycocyanin-conjugated TiO2-doped Fe3O4 magnetic nanoparticles (Pc-Ch-TiO2-Fe3O4 NPs) for cell adhesion, and their potential was analytically characterised using FESEM, EDX, XRD, FT-IR, TGA, XPS, and VSM. RESULTS: Cell separation efficiency, lactic acid yield, and kinetics were evaluated. Lactobacillus sp. were well-separated at an optimum concentration of 40 mg/100 mL using Pc-Ch-TiO2-Fe3O4 NPs, with a cell separation efficiency of 71.69%. The consistency of the Pc-Ch-TiO2-Fe3O4 NPs was again tested in a 5-L lab fermentor, leading to a lactic acid concentration of 23.65 g L-1 after 48 h in the third cycle. These findings confirm the method's suitability for separating Lactobacillus sp. and highlight the strain's robust fermentative performance across three consecutive batch cycles. Kinetic studies comprised a linear fit of the Contois model with μmax (h-1) = 0.47 and Ks = 3.855 in the initial cycle. DISCUSSION: The investigation found that Pc-Ch-TiO2-Fe3O4 nanoparticles may effectively separate and retain Lactobacillus sp. in batch fermentation systems. In addition to enabling efficient magnetic cell recovery, the nanoparticles help to improve downstream processing by increasing the purity of lactic acid. This method is a viable alternative to traditional separation methods, enabling sustainable and cost-effective industrial bioprocessing.